Servlet-自動頁面重新整理

考慮一個網頁，它顯示直播比賽分數或股票市場狀態或貨幣兌換率。對於所有這類網頁，你需要使用瀏覽器的重新整理或重新載入按鈕定期重新整理你的網頁。

Java Servlet透過向你提供一種機制，讓你可以製作一個網頁，它將按給定的時間間隔自動重新整理，從而簡化了這項工作。

重新整理網頁最簡單的辦法是使用響應物件的setIntHeader()方法。以下為該方法的簽名-

public void setIntHeader(String header, int headerValue)

該方法將標頭“重新整理”傳送回瀏覽器，同時附帶一個整數值，該值指示所涉及的秒數。

自動頁面重新整理示例

此示例演示Servlet如何使用setIntHeader()方法設定重新整理標頭來執行自動頁面重新整理。

// Import required java libraries
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;
 
// Extend HttpServlet class
public class Refresh extends HttpServlet {
 
   // Method to handle GET method request.
   public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
      
      // Set refresh, autoload time as 5 seconds
      response.setIntHeader("Refresh", 5);
 
      // Set response content type
      response.setContentType("text/html");
 
      // Get current time
      Calendar calendar = new GregorianCalendar();
      String am_pm;
      int hour = calendar.get(Calendar.HOUR);
      int minute = calendar.get(Calendar.MINUTE);
      int second = calendar.get(Calendar.SECOND);
      
      if(calendar.get(Calendar.AM_PM) == 0)
        am_pm = "AM";
      else
        am_pm = "PM";
 
      String CT = hour+":"+ minute +":"+ second +" "+ am_pm;
    
      PrintWriter out = response.getWriter();
      String title = "Auto Page Refresh using Servlet";
      String docType =
         "<!doctype html public \"-//w3c//dtd html 4.0 " + "transitional//en\">\n";
      
      out.println(docType +
         "<html>\n" +
         "<head><title>" + title + "</title></head>\n"+
         "<body bgcolor = \"#f0f0f0\">\n" +
         "<h1 align = \"center\">" + title + "</h1>\n" +
         "<p>Current Time is: " + CT + "</p>\n"
      );
   }
   
   // Method to handle POST method request.
   public void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
      
      doGet(request, response);
   }
}

現在讓我們編譯上述Servlet並在web.xml中建立以下條目

....
 <servlet>
     <servlet-name>Refresh</servlet-name>
     <servlet-class>Refresh</servlet-class>
 </servlet>
 
 <servlet-mapping>
     <servlet-name>Refresh</servlet-name>
     <url-pattern>/Refresh</url-pattern>
 </servlet-mapping>
....

現在使用URL https://:8080/Refresh呼叫此Servlet，該URL將每隔5秒以當前系統時間顯示。只要執行Servlet並等待檢視結果 -

Auto Page Refresh using Servlet

Current Time is: 9:44:50 PM

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